D Liu

SU-E-P-48: Evaluation of Intensity Modulated Radiotherapy (IMRT) with Three Different Commercial Planning Systems for the Treatment of Cervical Cancer

Purpose: To investigate the performances of three commercial treatment planning systems (TPS) for intensity modulated radiotherapy (IMRT) optimization regarding cervical cancer. Methods: For twenty cervical cancer patients, three IMRT plans were retrospectively re-planned: one with Pinnacle TPS,one with Oncentra TPS and on with Eclipse TPS. The total prescribed dose was 50.4 Gy delivered for PTV and 58.8 Gy for PTVnd by simultaneous integrated boost technique. The treatments were delivered using the Varian 23EX accelerator. All optimization schemes generated clinically acceptable plans. They were evaluated based on target coverage, homogeneity (HI) and conformity (CI). The organs at risk (OARs) were analyzed according to the percent volume under some doses and the maximum doses. The statistical method of the collected data of variance analysis was used to compare the difference among the quality of plans. Results: IMRT with Eclipse provided significant better HI, CI and all the parameters of PTV. However, the trend was not extension to the PTVnd, it was still significant better at mean dose, D50% and D98%, but plans with Oncentra showed significant better in the hight dosage volume, such as maximum dose and D2%. For the bladder wall, there were not notable difference among three groups, although Pinnacle and Oncentra systems provided a little lower dose sparing at V50Gy of bladder and rectal wall and V40Gy of bladder wall, respectively. V40Gy of rectal wall (p=0.037), small intestine (p=0.001 for V30Gy, p=0.010 for maximum dose) and V50Gy of right-femoral head (p=0.019) from Eclipse plans showed significant better than other groups. Conclusion: All SIB-IMRT plans were clinically acceptable which were generated by three commercial TPSs. The plans with Eclipse system showed advantages over the plans with Oncentra and Pinnacle system in the overwhelming majority of the dose coverage for targets and dose sparing of OARs in cervical cancer.

SU‐E‐P‐53: A Plan Quality Comparison for Volumetric‐Modulated Arc Therapy by Different Maximum Delivery Time Setting for Cervical and Upper Thoracic Esophageal Cancer

Purpose: To evaluate and compare the treatment plan quality of volumetric modulated arc therapy (VMAT) plans using different constrain conditions of delivery time for cervical and upper thoracic esophageal cancer. Methods: In this retrospective study, single-arc VMAT plans were generated with the Oncentra 4.3v system for twenty cervical and upper thoracic esophageal cancer cases. The maximum delivery time were set systematically various as 80s, 110s and 150s. Planning objectives were to deliver 60 Gy in 30 fractions to 95% of PTV, with maximum doses of spinal cord <45 Gy, V5Gy<50%, V10Gy<40%, V20Gy<25% and V30Gy<20% to the lung tissue. All of the three groups of VMAT plans were clinical acceptable. For plan evaluation statistics, PTVDmax, PTVDmin, PTVDmean, PTVD100∼D2, PTVV110∼V90, CordDmax, CordD2, CORDD40, LungDmean, LungV5∼V40 were analyzed and compared by SPSS 20.0. Results: The dose distribution quality of plans generated by different maximum delivery time settings was assessed by anova and non-parametric tests. No significant differences were found for target and OAR parameters except for the hight dose volume of PTV. The maximum dose (p = 0.034) and D2% (p = 0.030) of PTV in plans with 80s setting were detected significant lower than other plans by anova analysis. And for the maximum dose (p = 0.039) of PTV, it was showed the same results by non-parametric tests. Conclusion: Considering of the quality of VMAT plans and the treatment time, 80s as the initial parameters of the maximum delivery time would be a better choice than 110s and 150s for cervical and upper esophageal cancer.

SU‐E‐T‐164: Evaluation of Electron Dose Distribution Using Two Algorithms

PURPOSE To appreciate the difference of electron dose distributions calculated from the Monte Carlo and Electron 3D algorithms of radiotherapy in a heterogeneous phantom. METHODS A phantom consisted of two different materials (lungs mimicked by low-density cork and others by polystyrene) with an 11×16 cm field size (SSD = 100 cm) was utilized to estimate the two-dimensional dose distributions under 6 and 18 MeV beams. On behalf of two different types of tissue, the heterogeneous phantom was comprised of 3 identical slabs in the longitudinal direction with a thickness of 1 cm for each slab and 2 with a thickness of 2.5 cm. The Monte Carlo/MCTP application package constituted of five codes was performed to simulate the electron beams of a Varian Clinac 23IX. A 20×20 cm2 type III (open walled) applicator was used in these simulations. It has been shown elsewhere that the agreement of the phase space data between the calculation results of MCTP application package and the measured data were within 2% on depth-dose and transverse profiles, as well as output factor calculations. The electron 3D algorithm owned by Pinnacle 8.0m and the MCTP application package were applied for the two-dimensional dose distributions calculation. The curves at 50% and 100%-prescribed dose were observed for 6 and 18 MeV beams, respectively. RESULTS The MC calculations results were compared with the electron 3D calculations in terms of two-dimensional dose distributions for 6 and 18 MeV beams showed excellent agreement except in distal boundary where it was the very junction of the high and low-density region. CONCLUSIONS The Monte Carlo/MCTP method could be used to better reflect the dose variation caused by heterogeneous tissues. CONCLUSION A case study showed that the Monte Carlo/MCTP method could be used to better reflect the dose variation caused by heterogeneous tissues.

SU-E-T-35: An Investigation of the Accuracy of Cervical IMRT Dose Distribution Using 2D/3D Ionization Chamber Arrays System and Monte Carlo Simulation

PURPOSE The purpose of this work is to compare the verification results of three solutions (2D/3D ionization chamber arrays measurement and Monte Carlo simulation), the results will help make a clinical decision as how to do our cervical IMRT verification. METHODS Seven cervical cases were planned with Pinnacle 8.0m to meet the clinical acceptance criteria. The plans were recalculated in the Matrixx and Delta4 phantom with the accurate plans parameters. The plans were also recalculated by Monte Carlo using leaf sequences and MUs for individual plans of every patient, Matrixx and Delta4 phantom. All plans of Matrixx and Delta4 phantom were delivered and measured. The dose distribution of iso slice, dose profiles, gamma maps of every beam were used to evaluate the agreement. Dose-volume histograms were also compared. RESULTS The dose distribution of iso slice and dose profiles from Pinnacle calculation were in agreement with the Monte Carlo simulation, Matrixx and Delta4 measurement. A 95.2%/91.3% gamma pass ratio was obtained between the Matrixx/Delta4 measurement and Pinnacle distributions within 3mm/3% gamma criteria. A 96.4%/95.6% gamma pass ratio was obtained between the Matrixx/Delta4 measurement and Monte Carlo simulation within 2mm/2% gamma criteria, almost 100% gamma pass ratio within 3mm/3% gamma criteria. The DVH plot have slightly differences between Pinnacle and Delta4 measurement as well as Pinnacle and Monte Carlo simulation, but have excellent agreement between Delta4 measurement and Monte Carlo simulation. CONCLUSION It was shown that Matrixx/Delta4 and Monte Carlo simulation can be used very efficiently to verify cervical IMRT delivery. In terms of Gamma value the pass ratio of Matrixx was little higher, however, Delta4 showed more problem fields. The primary advantage of Delta4 is the fact it can measure true 3D dosimetry while Monte Carlo can simulate in patients CT images but not in phantom.

SU-E-J-248: Comparative Study of Two Image Registration for Image-Guided Radiation Therapy in Esophageal Cancer

PURPOSE Image-guided radiation therapy (IGRT) is one of the major treatment of esophageal cancer. Gray value registration and bone registration are two kinds of image registration, the purpose of this work is to compare which one is more suitable for esophageal cancer patients. METHODS Twenty three esophageal patients were treated by Elekta Synergy, CBCT images were acquired and automatically registered to planning kilovoltage CT scans according to gray value or bone registration. The setup errors were measured in the X, Y and Z axis, respectively. Two kinds of setup errors were analysed by matching T test statistical method. RESULTS Four hundred and five groups of CBCT images were available and the systematic and random setup errors (cm) in X, Y, Z directions were 0.35, 0.63, 0.29 and 0.31, 0.53, 0.21 with gray value registration, while 0.37, 0.64, 0.26 and 0.32, 0.55, 0.20 with bone registration, respectively. Compared with bone registration and gray value registration, the setup errors in X and Z axis have significant differences. In Y axis, both measurement comparison results of T value is 0.256 (P value > 0.05); In X axis, the T value is 5.287(P value < 0.05); In Z axis, the T value is -5.138 (P value < 0.05). CONCLUSION Gray value registration is recommended in image-guided radiotherapy for esophageal cancer and the other thoracic tumors. Manual registration could be applied when it is necessary. Bone registration is more suitable for the head tumor and pelvic tumor department where composed of redundant interconnected and immobile bone tissue.

SU‐E‐T‐513: Evaluation Output Dose of Electron Beams Based On Monte Carlo

Purpose: The purpose of this study is to investigate the influence factor of output dose for electron beams used in radiotherapy by Monte Carlo technique. Methods: MCTP code was used to calculate a group of output dose from Varian Clinac 23EX. According to the contributions, the calculated output dose was divided into four parts which can help to identify the physical reasons for the variation of output dose, dose from direct particles which was arisen from the machine head directly, dose from indirect particles which was arisen from the collimation devices, including jaws, scrapers and shielding. Results: 1. Appling same cones and same jsw settings but different field inserts, considering the 6 Mev beams, due to direct particles as well as indirect particles the output dose increases from the smallest to the largest field insert. 2. Different cones with same jaw settings and field size, for 6MeV electron beams, the use of a wider cone resulted in a higher output dose, which is mainly because of the direct particles. 3. Same field size with different cones and jaw settings, considering the 18 MeV beams, the wider cone exhibits a reduced output dose, which is attributed to indirect particles, and jaw contributes more than others. 4. Open cone, for the 6 MeV beams the wider cones that also has wider jaw settings showed an increased contribution to the output dose majorly from the indirect particles compared with the smaller cones. Similar trends were seen from the 9 MeV beams, although they were diminished. A reverse Result was indicated for the 18 MeV beams. Conclusion: The variation of output dose depends in a complicated manner on the characteristics of the beams and the modifications that the various cone‐insert combinations introduce to these characteristics.

SU‐E‐T‐712: Analyzing the Feasibility of the Margin From CTV to PTV for Esophageal Carcinoma with Retraction Method

Purpose: Discuss the feasibility of the retraction method by comparing with the Result of calculating methed about the margin from CTV to PTV based on the influence of target dosimetry of setup errors during esophageal carcinoma patients treatment. Methods: Forty two patients with esophageal cancer were treated by Elekta. The setup errors were measured six times during their treatment for once a week by EPID. The values of setup errors were simulated into the treatment planning system by moving the isocenter and then observing the dose distribution . The margin from CTV to PTV will be concluded both by the method of retracting (Fixed the PTV of the original plan, and retract PTV a certain distance defined as simulative organization CTVnx. The distance from PTV to CTVnx which get specified doses, namely guarantee at least 99% CTV volume can receive the dose of 95%, is the margin CTV to PTV we found) and the former formula method. Results: (1) The systematic setup errors of the 42 patients were −2.31mm left to right, −0.55mm anterior to posterior and −0.16mm superior to inferior, and the random errors were 4.42mm, 4.35mm and 4.48mm, respectively. (2)The setup errors resulted of a dose reduction of GTVD95 with 32cGy and CTVD95 with 88cGy. (3) The CTV to PTV margin by the retraction method based on our setup errors for esophageal cancer were 6mm left to right, 6mm anterior to posterior and 5mm superior to inferior, and 7.71mm left to right, 4.15mm anterior to posterior and 3.46mm superior to inferior by the formula method. Conclusion: The setup errors reduced the dose of GTV and CTV, the retraction method is more reliable than the formula method for calculating the margin from the CTV to the PTV, of which increasing a new method in this field.

SU‐E‐P‐22: Study of Dose Calculation Using Monte Carlo Method in Radiotherapy

PURPOSE Dose calculation using Monte Carlos MCTP (Monte Carlo Treatment Planning, MCTP, Fox Chase Cancer Center, FCCC) program in radiotherapy has been studied, and the accuracy of dose calculation and the clinical feasibility of MCTP program were evaluated. METHODS The original file of MCTP was compiled into 4 executable files in the Windows, (1)Monte Carlos MCTP MCBEAM was programmed to simulate the head of Varian Clinac 21EX linear accelerator using the Phase Space file. The data of the Phase Space was gotten under the condition of SSD=100cm. (2) The spectral analysis of the Phase Space file in the MCPLAN program was done for achieving the spectral distribution of accelerator 6MV-X ray. (3)The original MCTP program was modified in order to calculate this spectrum. (4)The percent depth dose (PDD) in the water phantom was calculated in the MCTP program, and displayed using the MATLAB software, then fit the measured data in the 3D water phantom. (5) Dose calculation in the inhomogeneity tissue was done under the square fields, and compared with the actual results by Dosemeters measurement and TPS calculation under the same conditions. RESULTS Using the linear accelerator spectrum, the calculated results of PDD curves in the water were well accorded with the measured curves. The reliability and accuracy of introducing spectrum in the MCTP program were approving. The precision of the dose calculation for the inhomogeneity tissue in the Monte Carlos MCTP program compared with the measured value and the TPS calculation was also well-pleasing. CONCLUSION Monte Carlos MCTP program could be applied to the dose calculation of tissue in radiotherapy.

SU‐E‐T‐716: An Investigation of Heterogeneity Dose Calculation Accuracy in IMRT from Five Commercial Treatment Planning Systems Useing Monte Carlo

Purpose: The goal of this study was to compare the accuracy of dose calculations relative to Monte Carlo calculations within a low‐density region of five common IMRT TPSs. Methods: Ten lungcancerIMRT cases were optimized with five different TPSs. Of the five TPSs we tested, Three use CSA/AAAs(Xio4.0, Pinnacle8.0m and Eclipse7.5.18.0) and two use PBAs(Corvus08, Eclipse7.5.18.0) dose calculation algorithms. All plans were designed for delivery on a Varian 23EX accelerator using 6MV photon beam. All plans were recalculated by Monte Carlo using leaf sequences and MUs for individual plans. Dose calculation algorithms were evaluated based on the criteria by Task Group 53. Profile doses, 2D dose distributions, point dose and Gamma index were compared. Results: The dose predicted in the target center met the criteria (±5% or ±3mm) for all TPSs compared to Monte Carlo calculated results; However, there were greater variations (from3.2% to10.7%) in the low‐dose region. The CSA/AAAs performed good agreement within the surrounding lung regions, even in the penumbral region compared with Monte Carlo methods. The CSA/AAAs greater than 95% pixels met the criterion at the ±7%/±7mm agreement level and more than 87% of the pixels still met even when the criterion was tightened to ±5%/±3mm. However, the agreement for the PBAs fewer than 66% pixels met the ±7% /±7mm criterion, with only 52% of the pixels meeting the ±5% /±3mm criteria. Conclusions: The Monte Carlo dose calculation system provides a platform for the fair comparison and evaluation of treatment plans to facilitate clinical decision making in selecting a TPS and beam delivery system for particular treatment sites. Based on our analysis, CSA/AAAs performs consistently and more accurately than PBAs when applied to IMRT planning involving low‐density regions.

SU-FF-T-193: An Investigation of the Accuracy of Esophageal IMRT Dose Distribution Using Three-Dimensional Dosimetry Techniques and Monte Carlo Simulation

Purpose: Complex dosedelivery techniques like intensity‐modulated radiation therapy(IMRT) require dose verification in three dimensions. This work investigates the accuracy of dose distribution of head‐and‐neck IMRT plans using three‐dimensional measurement and Monte Carlo simulation.Method and Materials: Eleven head‐and‐neck cases delivered by Varian 23EX were planned with Pinnacle 8.0. The plans were recalculated in the three‐dimensional measurement phantom Delta4 with the structures of every patients and accurate plans parameters. The plans were also recalculated by Monte Carlo using leaf sequences and MUs for individual plans of every patients and Delta4 phantom. All plans of Delta4 phantom were delivered and measured using Delta4. The dose distribution of iso slice, dose profiles, gamma maps and dose‐volume histograms were used to evaluate the agreement. Results: The dose distribution of iso slice and dose profiles from Delta4 measurement were in excellent agreement with both the Monte Carlo simulation and the Pinnacle calculation at all points. Gamma maps comparison show that all three distributions mutually agreed to within a 3% (dose difference) and 3mm (distance‐to‐agreement) criteria. A 93.2% gamma pass ratio was obtained between the Delta4 measurement and Pinnacle distributions with 3mm/3% gamma criteria. A 96.8% gamma pass ratio was obtained between the Delta4 measurement and Monte Carlo simulation with 2mm/2% gamma criteria and 99.2% gamma pass ratio with 3mm/3% gamma criteria. The DVH plot have slightly differences between Pinnacle and Delta4 measurement as well as Pinnacle and Monte Carlo simulation, but have excellent agreement between Delta4 measurement and Monte Carlo simulation.Conclusions: It was shown that Delta4 and Monte Carlo simulation can be used very efficiently to verify head‐and‐neck IMRTdelivery and no data is missed. The primary advantage of Delta4 is the fact it can measure true 3D dosimetry while Monte Carlo can simulate in patients CTimages but not in phantom.